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Michael Fidler’s SPARTAN 30 Headphone Amp/Line Preamplifier Might Be Ideal For a Desktop System

At $600, SPARTAN 30 promises low distortion volume control for use with active speakers or headphones.

Michael Fidler SPARTAN 30 headphone and line pre-amplifier Angle

Handmade in Kent, England the SPARTAN 30 Headphone Amp and Line Preamplifier. According to Michael Fidler (aka Classic Audio Ltd), the SPARTAN 30 provides a new look at traditional potentiometer-based preamplifiers. 

The SPARTAN 30 is a compact component that can replace traditional integrated amplifiers when used with active (powered) speakers.

The SPARTAN 30 features a sandblasted anodized aluminum cabinet.

Michael Fidler SPARTAN 30 high impedance headphone and line amplifier front

SPARTAN 30 Core Features

Volume Control: An active volume control circuit with a balanced output eliminates the need for extra circuitry on the line outputs for a shorter signal path with lower noise. Decreasing the value of the potentiometer from the more conventional 10kΩ to 5kΩ also reduces the noise power by a factor of two.

As volume is the most essential control in any sound system, care was taken sourcing the potentiometer used for that purpose.

Michael Fidler SPARTAN 30 volume

During development, all the conventional devices tested in the design failed to meet the channel tracking and lifespan requirements. A custom part rated for 5 million cycles and initially intended for industrial applications, was finally selected to be used in what would become the SPARTAN 30.  

Tech Note: Professional quality NJM5532 op-amps, mounted in turned IC sockets, are used for the line input and volume control stages. This supports a dynamic range of over 128dB with less than 5ppm distortion at 0dB gain and ±17V internal supply rails are used that can deliver over 21V RMS of undistorted output at the XLR connectors and tolerate 10.5V RMS maximum input. This makes overload unlikely even with the hottest source signals.

Reference: What is an Op-Amp?

Line Inputs: The SPARTAN 30 has three high-impedance RCA line inputs. This provides minimal insertion loss with both modern and vintage equipment. Input selection is performed via Panasonic relays right at the input connectors.

Michael Fidler SPARTAN 30 high impedance headphone and line amplifier rear

Headphone Output: The headphone output is optimized for most high-impedance headphones. NJM4556 high-current op-amps, found in some of the best Japanese equipment from the 1990s onwards are used in the supporting circuitry.

Separate chips for each channel working in parallel pairs provide over 700mW per channel for delivery to a 150Ω load.

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According to Michael Fidler, this reduces the noise from each amplifier section. The circuitry also operates as unity gain buffers which keeps distortion below 0.001% at 500mW output.

Michael Fidler logo

Tech  Note: In addition to the headphone output, the SPARTAN  30 also provided both RCA and XLR preamp outputs for connection to power speakers or an external audio system.

Power Supply: The power supply uses Panasonic electrolytic capacitors with precise diode references and an external transformer to keep hum-inducing magnetic fields from outside of the main enclosure.

Improved transformer magnetics limit standby power consumption to under 0.2W. It linear operation affords much better mains isolation than switching supplies and precludes switching noise from getting into the audio path.

Start-Up: A startup mute circuit operates three Panasonic telecom relays on the line and headphone outputs at start-up and switch-off. This limits unpleasant transients. When a jack is inserted into the headphone connector, the two-line output relays automatically mute the line output. 

Tech Note: This means you can’t listen to headphones and powered speakers/external audio system at the same time.

Michael Fidler SPARTAN 30 high impedance headphone and line amplifier top inside

Specifications

  • Product Type: Headphone Amplifier/Line Preamplifier Combination
  • Input Connections: Analog Line Inputs (3 Pairs RCA)
  • Output Connections: Heaphone (6.3mm -1/4-inch), Analog Line Outputs (1 pair RCA/1 pair XLR)
  • Gain Control Range: 17.5dB to -86dB (RCA), 23.5dB to -80dB (XLR)
  • Channel Balance (±0.3dB): -20dB to maximum gain
  • Frequency Response (0dB gain): 15Hz to 40kHz, ±0.1dB
    Output Noise (20Hz to 22kHz, 100Ω line source): -108.5dBV (0dB gain), -113.5dBV

Initial Impressions 

The Spartan 30 gets down to the basics – all analog (no digital connectivity or supporting DAC or ADC components). No wireless connectivity such as Bluetooth. Michael Fidler (through his Classic Audio Ltd company) puts the focus on the Volume Control as the main part of the Spartan 30 responsible for supporting the delivery of a clean listening experience.  

Availability and Pricing

The SPARTAN 30 is now available to order worldwide direct from Classic Audio Ltd. for £450 in the UK, €550 for EU countries, and $600 for the USA. 

Tech Note: GB 240V, EU 220V, and US/NEMA external transformers are supplied as standard to respective regions.

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